A drill chuck such as described in U.S. Pat. No. 4,836,563 for use with a tool having a shaft typically has a chuck body centered on and rotatable about an axis and an adjustment ring centered on the axis, rotatable about the axis on the chuck body, and axially fixed on the chuck body. The chuck body is formed with a plurality of angularly equispaced jaw-guide passages centered on respective jaw axes all lying on the surface of an imaginary cone centered on the axis. The adjustment ring is formed with a screwthread centered on the axis and exposed in the guide passages. Respective jaws displaceable in the passages along the respective axes are each formed with a row of teeth meshing with the screwthread so that relative rotation of the body and ring in one direction moves the jaws radially inward and axially forward and opposite relative rotation moves the jaws radially outward and axially rearward.
As described in commonly owned patent application Ser. No. 07/956,048 filed 2 Oct. 1992, now U.S. Pat. No. 5,236,206, such a chuck is often provided with a locking sleeve that is axially displaceable on the chuck body and engageable with teeth on the adjustment ring to limit its rotation. A spring urges the locking sleeve axially forward so its teeth mesh with those of the adjustment ring. A holding ring is limitedly rotatable on the body between a pair of angularly offset holding and freeing positions and is movable by a coupling ring so that in the freeing end position it pushes back the locking sleeve into a position out of mesh with the adjustment ring and in the holding end position it leaves the locking sleeve and adjustment ring in mesh.
To adjust such a clutch the holding ring is turned into the freeing position so that the locking sleeve is pushed back against the force of its spring and the adjustment ring is rotated.
PCT published application WO 91/12914 (based on German application P 40 05 757.7 filed 23 Feb. 1990 by W. Riebetanz et al), and also U.S. Pat. No. 5,174,588, describes such a system where the holding ring is outside of and freely rotatable relative to the locking sleeve which itself is not rotatable relative to the chuck body. The coupling is provided between the locking and holding rings and is constituted as an axially open cam recess formed in the locking sleeve and an axially projecting actuating lug formed on the holding ring. Thus in this arrangement the holding ring is only limitedly rotatable relative to the locking sleeve which in turn is non-rotatable on the chuck body.
The disadvantage of this structure is that when the chuck is operated keyless, that is wholly by hand without the use of a geared chuck key, it is necessary to grip the holding ring in one hand and the adjustment ring in the other hand to rotate them relative to each other. Such operation is fairly simple. When, however, the chuck is to be rotated by the drill motor to assist opening or closing of the jaws, it is necessary to hold the adjustment ring only, as the holding ring is going to rotate with the chuck body. This is somewhat tricky and can lead to injury to the user if he or she inadvertently grabs the holding ring also.